The present invention generally relates to a system for determining the deployed length of a flexible tension element such as cable, and more particularly, to a system which correlates the periodic displacement of a center wrap of a precision wound flexible tension element to a deployed length of the element.
The Navy has many applications which require the deployment of small diameter cables in the ocean. For example, the Navy deploys sensor arrays linked by fiber optic cables for monitoring ocean temperatures, salinity, current strength, and other physical properties. In order to optimize the life of the cable, the cable should conform to the sea floor so that it is not suspended over valleys. To achieve such conformance, it is desirable to know the deployed length of the cable.
In the past, deployed cable length was measured by feeding the cable through an odometer type mechanism that includes two wheels which counter-rotate as the cable is fed between them. An important limitation of the two-wheel type odometer system is that it generally cannot feed cable splices between the wheels. Therefore, the odometer type system is generally not suitable for applications requiring deployed lengths of cable in excess of that available from a single pack where cable from one pack, or spool must be spliced to cable from another pack. Also, this type of counter tends to be inaccurate and is cable specific. Another type of system for measuring deployed cable length relies on markers positioned at regular intervals along the cable. Such markers may include bar codes, magnetic spots, or metallic bands. A significant disadvantage of this type of system is that it requires additional manufacturing steps with associated costs to affix the markers along the cable.
A need therefore exists for a method for measuring the deployed length of a cable that can accommodate cable splices, is highly accurate, can be used on a wide range of cable diameters and designs, and which does not require markers. A non-contact method for determining the deployed length of a cable would be preferred.